Geothermal and Solar Thermal Systems
Did you know you can heat and cool your home basically for free, using energy right in the ground or from that abundant resource known as the sun?
Sure, there's an upfront cost to geothermal and solar-based heating and cooling systems, and it can be sizable. But with a 30 percent federal tax credit and other incentives, these systems can pay for themselves over time and provide you with free heating and cooling that’s natural, doesn’t rely on fossil fuels or emit any carbon dioxide.
A geothermal (ground-source) heat pump converts the heat of the earth into heat for your home. Consisting of a series of looped pipes drilled deep into the ground, a geothermal system works the same way a regular air-source heat pump does: by harvesting existing heat rather than creating it through combustion, as a gas furnace would.
Geothermal heating and cooling systems for homes are ground-and-water-source heat pumps that basically move heat from one area to another. This is not to be confused with geothermal plants that tap into the earth’s energy to produce electricity.
Geothermal systems for the home use the constant temperature of the ground, at about 45 to 75 degrees, to heat and cool areas of a home. In the winter, the warmth from the ground is brought into a heat pump to warm a home, and in the summer the heat is removed from the house, much in the same way a refrigerator works.
An indoor geothermal heat pump uses electrically driven compressors and heat exchangers to concentrate the Earth’s energy and release it inside the home at a higher temperature. In typical systems, duct fans distribute the heat to various rooms.
Costs start roughly at around $15,000 for a system capable of heating and cooling an average, 2,000-square-foot home. And much of that cost is in tapping the earth. Geothermal systems often require either vertical bore holes, dug several hundred feet deep, or horizontal arrays of piping placed 4 to 6 feet underground.
Horizontal arrays take up much more space, while several vertical wells may have to be dug for a home system. The depth of a well is dictated by how large the system must be to produce the amount of British thermal units (Btu) required to heat or cool your home. Polyethelyne tubing transports water or an antifreeze solution to the heat pump for use in the home.
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Systems also come in open or closed loops. Open loop systems use water from a well or pond to circulate through the system, then discharge the water through a different pipe. Closed loop systems keep the water or antifreeze sealed within the system. A standing column well can use a well also utilized for domestic water and return the used water via the same bore hole, potentially saving extra digging costs.
The type of system that's best for you will depend on your needs, the geography and geology (standing column wells are often used in the northeast, where there is bedrock close to the surface). A 350-foot-deep domestic use standing column well can develop approximately 5 tons of heat transfer.
When people think of solar thermal, they often think of water-based systems that heat tubes of fluid behind a glass panel to provide sun-warmed water for domestic use. A solar thermal system can also provide some home heating when used in conjunction with a radiant in-floor heating systems, though those systems can grow expensive.
What many people don't realize is that solar thermal can also heat air. A solar air heating panel can be mounted to a south-facing exterior wall, with a vent on the inside. The air heats up behind the glass solar panel, and a fan blows the warmed air into the room.
In some models the fan is even powered by the solar panels. It's a simple way to get heat right from the sun, and requires some mounting and a hole in your wall. A simple window air heater/collector can even be made for a few hundred dollars.
Solar Air systems are great for supplemental and space heating and can reduce your heating bills by as much as 30 percent, by heating your home naturally during the day. They can pay for themselves in a few years. The Solar Rating & Certification Corporation has ratings of these systems.